1. Field
The present invention relates to a laminate substrate having an aluminum carbide layer and a gallium nitride layer, and a method of fabricating the same. More particularly, the invention relates to a laminate substrate having a crystalline aluminum carbide layer formed thereon and a method of fabricating the same.
2. Discussion of the Background
A light emitting diode (LED) including a gallium nitride (GaN) based semiconductor may be used for various applications, such as signal devices, backlight units for liquid crystal panels, and the like. AlGaInN-based LEDs may have a wavelength band of 260˜290 nm or 360˜600 nm, and an AlGaN-based active layer may be included to produce a shorter wavelength band (300˜340 nm). As such, AlxGa1-xN-based semiconductor materials have been developed. At a wavelength of 280 nm, it is possible to obtain a light extraction efficiency of 10% or more.
However, since AlGaN is liable to split and has a relatively high dislocation density, an AlGaN material used in a wavelength band from 300 nm to 360 nm has not yet been developed. Current reports say that AlGaN-based LEDs exhibit a light extraction efficiency of at most 8%, in a wavelength band of 300˜350 nm.
Generally, elements located at an upper part of the periodic table emit light at shorter wavelengths. Although B, N or C has the shortest emission wavelengths, these components are not suited for general light emitting materials, since the growth of these materials requires high temperatures of 2500° C. or more. AlN may be used instead of these materials. Accordingly, investigations have been made to develop a material that emits light at a short wavelength (λ=210 nm) using AlN. However, AlGaN has low light extraction efficiency, as described above.
Meanwhile, aluminum carbide Al4C3 (hereinafter, “AlC”) is an important compound in aluminum related technology, due to its high electrical resistance and high thermal conductivity at room temperature. Since AlCN, which is an aluminum compound similar to AlC, can be used in various applications such as microelectronics, photonic technology and the like due to its wide band gap, high chemical stability and high hardness, AlC is also anticipated to have the same capabilities as AlCN. AlC is a III-IV group-based material and is generally known as a nano-processing material.
In order to use AlC for a semiconductor substrate, particularly, for LEDs, it is necessary to provide a thin film exhibiting excellent crystallinity. However, crystalline thin films formed using AlC have not yet been developed. Currently, only a non-crystalline thin film of AlC has been reported by L. Yate et al., Surface and Coatings Technology, 203, 1904 (2009).